Compositions which can be crosslinked by ultraviolet light and which are based on (a) an organopolysiloxane having an acryloxy group and containing triorganosiloxane units of the formula EQU H.sub.2 C.dbd.CHCOOR"SiR'.sub.2 O.sub.1/2
in which R' represents the same or different monvalent hydrocarbon radicals which are free of aliphatic double bonds, and R" represents a divalent hydrocarbon radical, in which at least 80 percent of the siloxane units other than the triorganosiloxane units are diorganosiloxane units in which in both siloxane units SiC-bonded organic radicals are monovalent hydrocarbon radicals free of aliphatic double bonds, (b) a filler having a specific surface area of at least 50 m.sup.2 /g, and (c) a photoinitiator are described in European Patent Application No. EP-OS 152,179 to Loctite Corporation.
It is, therefore, an object of the present invention to provide compositions which can be crosslinked by radiation to form elastomers. Another object of the present invention is to provide a crosslinkable composition containing (a) an organopolysiloxane having triorganosiloxane units, (b) a filler having a surface area of at least 50 m.sup.2 /g, and (c) a photoinitiator, if desired, and which can be crosslinked by radiation. A further object of the present invention is to provide a composition which can be crosslinked rapidly and at room temperature by ultra-violet light, and which, on crosslinking, form elastomers having especially good physical properties such as high tear strength and high tear propagation resistance.